Topic 3 Revision - Energy Flow - GCSE Edexcel B2

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Topic 3 Revision ­ Energy Flow
Plant and animal cells are similar
b ecau se
they cont
a i
n nuclei,
cytoplasm an d
a membrane.
Plant cells als
ha ve cellulose cell walls,
chloroplasts cont
a i
ning chlorophyll and
a vacuole.
A cell that is found in the leaf of a plant:
ANIMAL CELLS: Do not contain a cell wall, chlorophyll or a vacuole.
PHOTOSYNTHESIS: Carbon dioxide + Water Glucose + Oxygen
Light energy is absorbed by a chemical called chlorophyll, this energy is used to help make glucose for respiration.
For plants to grow they need to photosynthesise during the day and respire all the time.
1. Human exploitation of plants, including their use as a food source
2. Analysis of data and conclusion of the effects of limiting factors on the rate of photosynthesis.
Apparatus which could be used to find out if light affected the amount of gas produced by a water plant.
The effect of the variables on the rate of photosynthesis:

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Conditions for optimum growth are with all three variables at a medium level. These factors are known as limiting
Light intensity:
Increased light intensity increases rate of photosynthesis until the rate levels off, until then light is the limiting
factor after that another factor is in short supply.
Reducing limiting factors:
TEMPERATURE ­ Optimum temperature maintained by appropriate heating/cooling method
CARBON DIOXIDE ­ Increase carbon dioxide in air by e.g.…read more

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DENITRIFYING BACTERIA: Converts nitrate into nitrogen gas.
Could a Biosphere be used to Colonise Mars?
Biosphere II was built in America in 1989. Scientists wanted to find out if humans and other living things could live i
Biosphere II without any help from the outside world. If the experiment worked, then scientists thought it might be
possible to build a biosphere on Mars.…read more

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Why are rainforests being destroyed?
Farming of cattle
Planting crops
Providing fuel
Clearing for building, houses or roads
Impact of Deforestation on the Environment:
Loss of habitat /places to live
Atmospheric CO2 levels increase (from burning/rotting/reduced photosynthesis), increased global
warming/greenhouse effect
Increases soil erosion/increased leaching of minerals/nutrients
Increases desertification
Rivers get silted
Increased flooding
Reduces biodiversity/species become extinct
Why is food unequally distributed throughout the world?
The climate in some parts of the world does not favour food production
Some countries are too poor…read more


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